Vaillant HE ( Condensing ) Pressure problem COMBI

[Systemfix]

Hi Guys
before you have a go ive checked the FAQ's and cant find the remedy
I have a HE combi that has an anoying problem, the pressure keeps dropping itself and the baffling thing is that its not letting water outside?? there is also no evidence of a leak inside on any of the rads (even underfloor) which ive also checked, all pipework is sound. Has to be topped up nearly everyday, We dont have dripping taps either so what could be the cause of it, boiler is around 7 years old
Any pointers would be great
Thanks in advance

 

[gas4you]

Pressurise boiler as normal. Isolate at ch valves under boiler and leave for as long as possible.

If the pressure remains constant then leak is on heating system and not boiler. This will also be shown by the pressure dropping when you open the valves again.

Failing that, check whether the condensate drain is dripping even when the boiler is not on.

There have been a few cases of the main HE leaking, but rare.

 

[Systemfix]

Cheers Dave good advice there, ive checked the condensate pipe and prv pipe and bone dry all the time, could there be something wrong with the boiler as the heating circuit has been completely checked throughout but will try that test anyways, thanks for your help